Someone could explain this better than I but, at a 100,000ft view, when you put all of these queries in a single transaction, the data isn't actually written as you would think until the transaction is committed. When that happens, it's done as a single transaction from the Log file to the table. It's a tried and true method to make WHILE loops run a bit faster although it does extend the time for locks taken. Generally, such single-ton updates should be avoided.